Acrylic synthetic fibers having improved properties and process for producing the same

ABSTRACT

ACRYLIC FIBERS CONTAINING STREAKY INCLUSIONS OF 2-25% POLYVINYL CYANOETHYL ETHER OF DS VALUE BETWEEN 55% AND 75% HAVING IMPROVED LUSTER, SOFTNESS, HYGROSCOPIC, AND ANTISTATIC PROPERTIES. SUCH FIBERS ARE MADE BY WET-SPINNING A SOLUTION OF THE POLYVINYL CYANOETHYL ETHER AND THE ACRYLONITRILE POLYMER IN A COMMON SOLVENT, WATER-WASHING, STRETCHING, AND DRY-HEAT DRYING THE FIBERS SO SPUN.

United States Patent C 3,698,994 ACRYLIC SYNTHETIC FIBERS HAVING IM-PROVED PROPERTIES AND PROCESS FOR PRODUCING THE SAME Keitaro Shimoda andIsamu Obama, Okayama, Japan, assignors to American Cyanamid Company,Stamford,

onn. No Drawing. Filed Jan. 27, 1971, Ser. No. 110,293 Int. Cl. D02g3/00; C08f 29/56 US. Cl. 161-178 10 Claims ABSTRACT OF THE DISCLOSUREAcrylic fibers containing streaky inclusions of 225% polyvinylcyanoethyl ether of DS value between 55% and 75% having improved luster,softness, hygroscopic, and antistatic properties. Such fibers are madeby wet-spinning a solution of the polyvinyl cyanoethyl ether and theacrylonitrile polymer in a common solvent, water-washing, stretching,and dry-heat drying the fibers so spun.

This invention relates to acrylic fibers containing distributed thereina poly(vinyl cyanoethyl ether) as a separate phase continuous throughoutthe fiber length, said polyether phase being detached from saidpolyacrylonitrile phase and separated therefrom by void space. Theinvention also relates to a process by which the desired fibres areobtained.

In particular, this invention relates to acrylic fibers in whichimprovements in hydroscopic, antistatic, lustrous and softnessproperties are obtained. The process involves wet-spinning a polymersolution comprising a blend of an acrylonitrile polymer and apolyl(vinyl cyanoethyl ether) wherein during the spinning procedure aphase separation of polymers occurs with the result that the poly(vinylcyanoethyl ether) is distributed within said fiber as a separate phasecontinuous throughout the fiber length detached from the acrylonitrilepolymer and separated therefrom by void space. The resulting fiberpresents an appearance in which the poly-(vinyl cyanoether) tends to beseen as a streak-like dispersion within the fiber.

It is known in the prior art that improvements in acrylic fiberproperties can be achieved by blending a poly(vinyl cyanoethyl ether)with an acrylonitrile polymer. For example, in US. Pat. 2,938,008, May24, 1960, Hare, there is disclosed a fiber of improved properties, whichfiber is based on a homogenous blend of an acrylonitrile polymer and apoly(vinyl cyanoethyl ether). The property improvements resulting are inabrasion resistance, antifibrillation, and dyeability. In thisreference, the polymers are not only mutually soluble in the polymersolvent but are compatible with one another in fiber form. The propertyimprovements resulting are those associated with a homogeneousdistribution of polymers throughout the fiber structure and there is nophase separation of the compatible polymers.

In accordance with the product aspect of the present invention there isprovided an acrylic fiber comprising an acrylonitrile polymer and apoly(vinyl cyanoethyl ether), said ether being present in an amountranging from about 2% to 25%, by weight, based on the total weight ofthe fiber and being distributed as a separate phase within said fiber,said ether phase extending continuously throughout the fiber length andbeing detached from said acrylonitrile polymer and separated therefromby void space, the poly(vinyl cyanoethyl ether) being etherified withcyanoethyl groups to an extent which is between about 55% and 75 of fulltheoretical etherification with acrylonitrile.

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In accordance with the process aspect of the present invention there isprovided a procedure for preparing the above-described fibers whichcomprises preparing a homogeneous spinning solution in a suitablepolymer solvent of an acrylonitrile polymer and from about 2% to 25%, byweight, based on the total weight of polymer in said solution of apoly(vinyl cyanoethyl ether) which is etherified to an extent which isfrom about 55% to 75 of full theoretical etherification withacrylonitrile, wet-spinning said polymer solution into a coagulant forsaid polymers, washing the coagulated wet-gel filament thus formed,stretching the wet-gel filament, and drying the stretched filament.

The fibers of the present invention are improved over conventionalacrylic fibers in such properties as luster, hydroscopicity, andsoftness and have a reduced tendency to accumulate static electricalcharges. The fibers exhibit the appearance of having a streakydispersion of the poly(vinyl cyanoethyl ether) therein although saidpolyether is dispersed as a separate phase within the fiber extendingcontinuously throughout the fiber length as a separate phase detachedfrom the acrylonitrile polymer phase and separated therefrom by voidspace.

As the acrylonitrile polymer that may be employed in the presentinvention are included those conventional fiber-forming acrylonitrilepolymers and copolymers which contain at least by weight ofacrylonitrile. A mixture of two or more such polymers may also beemployed. Numerous vinyl type monomers are known which arecopolymerizable with acrylonitrile and provide desirable fiber-formingcopolymers. Such vinyl type monomers may be employed singly or inmixture with acrylonitrile so long as their total concentration in thecopolymer does not exceed about 30% by weight.

As the poly(viny cyanoethyl ethers) useful in the present invention arethose having the formula wherein m+n represents the total content of thepolymer and m represents from about 55 to about of the total content andR represents hydrogen or an acetyl group. The molecular weight of thepolymer may vary widely and is not critical. Typically, polymerscorresponding to those wherein the unsubstituted polyvinyl alcohol has amolecular weight in the range of about 10,000 to about 100,000 areemployed.

A customary procedure for obtaining a poly(vinyl alcohol) is bypolymerizing vinyl acetate and subsequently saponifying the resultingpolymer. The percentage of hydroxyl groups produced will depend upon thedegree to which saponification is effected. To obtain the cyanoethylether, the saponified poly(vinyl acetate) is reacted with acrylonitrileunder alkaline conditions and, since such conditions also effectsaponification, it is possible to efiect saponification andetherification concurrently. Thus, the useful poly(vinyl cyanoethylethers) are readily obtained by controlled saponification andetherification of poly (vinyl acetate). As stated above, the usage ofpoly(vinyl cyanoethyl ether) must be between about 2% to 25%, by weight,based on the total polymer weight.

If the value of m in the formula given above is less than about 55%, thepoly(vinyl cyanoethyl ether) is dissolved out of the extruded filamentin the coagulating bath, in the washing step immediately following, orboth and will not be present in the final fiber. On the other hand, ifthe value of m is greater than about 75%, the poly(vinyl cyanoethylether) will become compatible with the acrylonitrile polymer and thedesired separate and detached phase will not be obtained. If the contentof poly(vinyl cyanoethyl ether) is less than about 2%, by weight, basedon the total polymer weight, such content does not effect anysignificant improvements in the resulting fiber properties. On the otherhand, if the content of poly(vinyl cyanoethyl ether) is above about 25%,by weight, based on the total polymer weight, the swollen gel fibersupon drying, regardless of drying temperature, tend to stick together,apparently due to inability to confine the poly(vinyl cyanoethyl ether)as a separate phase within the fiber.

As the solvent for preparing the spinning solution of the polymers, onemay use organic solvents or inorganic salt and inorganic acid solvents.As organic solvents, for example, one may use dimethyl formamide,dimethyl acetamide, and dimethyl sulfoxide. As inorganic salt solventsfor example, one may use concentrated aqueous solutions of thiocyanates,such as sodium, potassium, ammonium, and calcium thiocyanates andmixtures thereof, concentrated aqueous solutions of zinc chloride, andconcentrated aqueous solutions of lithium chloride. As inorganic acidsolutions, for example, one may use concentrated aqueous nitric andsulfuric acids.

As the coagulant for the spun polymer solution, typically one uses thoseliquid coagulants normally employed in-wet-spinning, taking into accountthose subtle relationships between polymer solvent and coagulant as arewell known in the art. Among the suitable coagulants, for example, arewater, aqueous solutions of the above-mentioned inorganic salts or acidsin which the concentration of salt or acid does not exceed 20% by weightthereof, aqueous solutions of the above-mentioned organic solvents inwhich the concentration of organic solvent is in the range of 20% to 70%by weight thereof, or polyethylene glycol.

In carrying out the process of the present invention, a spinningsolution is prepared by dissolving the acrylonitrile polymer andpoly(vinyl cyanoethyl ether) in the selected solvent. Preferably, thissolution is prepared by first dissolving the poly(vinyl cyanoethylether) in at least a portion of the selected solvent and then adding theacrylonitrile, while making any necessary adjustment as to solventcontent. It is generally preferable to adjust the polymer content of thespinning solution to between about and 30%, by weight, based on thetotal weight of the spinning solution. However, it is not necessary torestrict the polymer content of the spinning bath to this specific rangesince such factors as solution viscosity, tem perature of the spinningsolution, and solvent nature influence the useful polymer concentrationsin specific instances.

The polymer solution is wet-spun into an appropriate coagulant accordingto conventional procedures. Following coagulation, the filaments arewashed, stretched and dried in accordance with conventional procedures,except that the drying temperature should not exceed about 115 C., sincedrying of the wet-gel filaments at higher temperatures tends to causethe fibers to stick together. Subsequent to drying other conventionalsteps normally employed may be carried out as desired.

Although it is not known for certain what mechanism is responsible forthe fibers of the present invention and the inventors do not wish to bebound by any particular theory, the following theory is suggested. Bothpolymers are coagulated by the coagulating bath as it penetrates intothe extruded polymer solution but the rate of coagulation differs amongthe two polymers. The acrylonitrile polymer coagulates first uponcontact with the coagulant and forms the outer periphery of the wet gelfilament. Since the poly(vinyl cyanoethyl ether) is incompatible withthe coagulated acrylonitrile polymer and is not immediately precipitatedby the coagulant, the poly(vinyl cyanoethyl ether) in solution form isdisplaced toward the center of the filament by the penetrating coagulantand the increasing content of coagulated polyacrylonitrile building upwithin the peripheral wall of the gel filament. Although the coagulantcan penetrate the porous nature of the gel filament, the poly(viny1cyanoethyl ether) is incapable of such penetration and remains withinthe gel structure. Eventually, as coagulation continues the poly (vinylcyanoethyl ether) is coagulated within the fiber as a separate phasefrom the acrylonitrile polymer but, because the poly(vinyl cyanoethylether) remained as an interconnected solution within the gel filament,the poly (vinyl cyanoethyl ether) phase remains connected along thelength of the formed filament. As first formed, the separate poly(vinylcyanoethyl ether) phase is joined to the inner portion of theacrylonitrile phase. Subsequently, after washing, stretching, anddrying, due to differences in the swollen states of the polymers anddifferential shrinkages thereof, the poly(vinyl cyanoethyl ether) becomes detached from the acrylonitrile polymer and void space formsbetween the polymer structures. This ultimate structure is felt to giverise to the streaky dispersion effect noted. It is also felt that theunique structure of the fiber gives rise to the improved propertiesnoted.

The invention is further illustrated by the examples which follow, inwhich all parts and percentages are by weight unless otherwisespecifically noted.

The various tests by which the data recorded in the following examplesare obtained are conducted as follows.

(1) K/S value 1.5 grams of the fiber to be measured are immersed in asolution at 70 C. of the following:

Percent C.I. Basic Blue 22 0.5

Acetic acid 1.0 Sodium sulfate 10.0

wherein the percentages are based on the weight of fibers. The volume ofsolution is 50 times the weight of fibers. Upon immersion of the fibers,the bath is heated to 100 C. at the rate of 1 C. per minute and the bathis then maintained at 100 C. for 30 minutes. The fibers are thengradually cooled in the bath, removed, and dried. One gram of the dyedfibers are then taken and the reflectance determined using a source ofmonochromatic light. The K/S value is determined from the Kubelka-Munkequation:

K/S=(1-R) /2R wherein R is the reflectance measured, K is the absorptioncoeflicient of the fibers, and S is the scattering coefiicient of thefibers.

The K/ S value quantitatively represents the magnitude of the internalreflecting surface area and smaller K/S values indicate larger internalreflecting surface areas. Thus, the K/S value indicates the degree ofstreaky dispersion formed within the fibers by the poly(vinyl cyanoethylether).

(2) 60-degree mirror surface luster (G Samples of fiber from any crimphas been removed are arranged in parallel and laid flat on a cardboardto present a rectangular fiber surface of size 6 centimeters by 4.5centimeters. The G value is then determined according to the methoddescribed in HS 2-8741 using a GM-5 luster meter (manufactured byMurakami Color Technical Laboratory). Measurements of luster wereobtained with the angle of incidence parallel to the axial direction ofthe fiber.

(3) Hygroscopicity About two grams of fibers to be measured are predriedfor one hour at C. and then conditioned at 20 C. and 65% relativehumidity for 24 hours. The conditioned fibers are Weighed and the weightdesignated A. The fibers are then dried for 20 hours at 60 C. at apressure equivalent to 50 millimeters of mercury em ploying a vacuumdryer containing phosphorus pentoxide. The fibers thus dried are Weighedand the weight designated B. The hygroscopiclty is calculated from thefollowing formula employing the weights designated above:

Hygroscopicity (percent) X 100 (4) Antistatic activity The fibers areconditioned for 16 hours at 20 C. and 65% relative humidity. Theelectrical resistivity of the fiber surface is then measured using anappropriate meter (Textrome Model GR-54, manufactured by Chuo ElectronicIndustrial Company, Ltd.).

(5) Water-absorption length Fibers to be measured are spun into a 36cotton count single yarn having 325 twists per meter. Two such singleyarns are plied employing 540 twists per meter in plying. The yarn thusobtained is knitted into a plain weave fabric having a weight of 200milligrams per square centimeter. A test specimen 3 centimeters wide and12 centimeters long is cut from the fabric. The test specimen is hungvertically at a fixed height with its lower end held submerged in awater tank by tension. The test is conducted in a conditioned room at 20C. and 65 relative humidity employing water at 20 C. After the specimenhas been maintained in the position stated for minutes, the height towhich water has risen in the fabric is measured and reported. In theevent the height exceeds 95 millimeters within the ten minute timelimit, the testing is modified so that the time required to reach the 95millimeter height is reported.

EXAMPLE 1 A ploy(vinyl acetate) which has been saponified to an extentwhich exceeds 95% is employed in preparing a poly(vinyl cyanoethylether). One part of the resulting poly(vinyl alcohol), which has adegree of polymerization of 1700, i.e. a molecular weight of about75,000, is dissolved in 10 parts of 1% aqueous sodium hydroxidesolution. To this solution are added 3 parts of acrylonitrile and themixture is stirred and reacted at 50 C. for 150 minutes. The reactionmixture was then filtered, the filter cake washed with water andrecovered. There was obtained a poly(vinyl cyanoethyl ether) whichcontained 60.2% of the full theoretical content of cyanoethyl groups.The resulting polymer contained water in the amount of 45%.

In 7.2 parts of 60% aqueous sodium thiocyanate solution was dissolved 1part of the poly(vinyl cyanoethyl ether.) obtained above. As theacrylonitrile polymer there was employed a copolymer of the followingmonomer composition:

Percent Acrylonitrile 91 Methyl acrylate 8.73 Sodium methallylsulfonate0.27

9 parts of this polymer and 6.9 parts of water were added to thesolution of poly(vinyl cyanoethyl ether) and stirred to obtained auniform slurry. To the slurry was then added 24.1 parts of 60% aqueoussodium thiocyanate solution and the mixture was stirred at 60 C. for 75minutes to obtain a clear solution. The solution obtained, which had aratio of acrylonitrile polymer to poly(vinyl cyanoethyl ether) of 90:10,was then heated to 70 C., spun through a spinnerette into an aqueouscoagulation bath which consisted of a 12% aqueous solution of sodiumthiocyanate maintained at a temperature of -3 C. The filaments thusformed were waterwashed while being stretched at a stretch ratio of 2:1,further stretched at a stretch ratio of 5:1 in boiling water and thendried at 90 C. The dried fibers were then relaxed of an atmosphere ofsteam at 115 C. to produce acrylic fibers in the present invention.

Comparative Example A In this example, the acrylonitrile polymer ofExample 1 was the sole polymer in spinning fibers. 10 parts of theacrylonitrile polymer of Example 1 were dissolved in parts of a 48%aqueous sodium thiocyanate solution. The spinning solution thus obtainedwas spun into filaments following the procedure of Example 1. Thecoagulated filaments were water-washed and stretched as in Example 1.The stretched fibers were dried at a dry bulb temperature of 120 C. at20% relative humidity and then relaxed in an atmosphere of steam at 120C. for 10 minutes.

Properties of the fibers obtained in Example 1 and Comparative Example Aare given in Table I which follows.

TAB LE I Fibers From Comp. Property Example 1 Example A K/S value 0.9971.600 Hygroscopicity, percent 3.0 1. 8 60-degree mirror surface luster(G580) 48 33 Surface resistivity, ohms. 10 10 B EXAMPLE 2 One part ofthe poly(vinyl cyanoethyl ether) prepared in Example 1 was dissolved in4.8 parts of 60% aqueous sodium thiocyanate solution. To this solutionwere added 4.6 parts water and 5.7 parts of a copolymer containing 45%water and having the following monomer composition:

Percent Acrylonitrile 91 Methyl acrylate 8.73 Sodium methallylsulfonate0.27

The mixture was stirred to form a slurry and then 16.1 parts of 60%aqueous sodium thiocyanate solution were added and the mixture stirredfor 75 minutes while mainmining the temperature of 60 C. so that ahomogeneous solution was obtained. The ratio of acrylonitrile polymer topoly(vinyl cyanoethyl ether) was 85:15. The solution was then heated to70 C. and spun through a spinnerette into a coagulating bath of 12%aqueous sodium thiocyanate maintained at 3 C. The filaments thusobtained were water-washed and concurrently stretched at a stretch ratioof 2X. The filaments were then further stretched in boiling water at astretch ratio of 5X. After stretching, the fiber was dried at 115 C. andthen relaxed in an atmosphere of steam at 115 C. Properties of thefibers obtained are given in Table II.

TABLE II Property:

K/S value 0.701. Hygroscopicity 5.5%. G, 41. Surface resistivity 10ohms. Water absorption 3 min. 50 seconds for millimeter height.

When the fibers of Comparative Example A were tested for waterabsorption, it was found that the length was only 76 millimeters after10 minutes.

EXAMPLE 3 Following the procedure of Example 1 a poly(vinyl cyanoethylether) was prepared. In this example, the

amount of acrylonitrile employed in forming the ether was 2.4 parts perpart of poly(vinyl alcohol). There was obtained a poly(vinyl cyanoethylether) which contained 55.2% of the full theoretical content ofcyanoethyl groups.

Employing this poly(vinyl cyanoethyl ether), fibers were preparedfollowing the procedure of Example 2. Fiber properties are given inTable III.

Comparative Example B The procedure of Example 3 was followed exceptthat the amount of acrylonitrile employed was 1.8 parts per part ofpoly(vinyl cyanoethyl ether) which contained 49.7% of the fulltheoretical content of cyanoethyl groups.

Employing this poly (vinyl cyanoethyl ether), fibers were preparedfollowing the procedure of Example 2. Fiber properties are also given inTable III.

TABLE III Comp. Exam- Exam- Property pie 3 ple B K/S value 1.0 1. 5 G.40 27 The data indicate that when the poly(vinyl cyanoethyl ether) has49.7% of the full theoretical content of cyanoethyl groups, the fibersobtained do not possess the desired streaky dispersion effect or luster.The data also indicate that a poly(vinyl cyanoethyl ether) having 55.2%of the full theoretical content of cyanoethyl groups produces thedesired properties.

EXAMPLE 4 1.8 parts of the poly(vinyl cyanoethyl ether) obtained inExample 1 were dissolved in 40 parts of dimethyl formamide. To thissolution were added 9 parts of a dried powdered copolymer obtained froma monomer content of:

Parts Acrylonitrile 91 Methyl acrylate 8.73 Sodium methallylsulfonate0.27

The mixture was stirred for 120 minutes at 50 C. to prepare ahomogeneous spinning solution. The spinning solution at 50 C. spun intoa coagulation bath maintained at 70 C. and consisting of polyethyleneglycol of molecular weight 400. The filaments thus obtained werestretched at a stretch ratio of 5x in a bath of polyethylene glycol ofmolecular weight 600 and maintained at 120 C. The filaments were thenwater-washed at room temperature and dried at 115 C. The fibers werethen relaxed in an atmosphere of steam at 120 C. Properties of thefibers obtained are given in Table IV.

This example shows the usefulness of an organic polymer solvent in thepresent invention.

EXAMPLE 5 One part of the poly(vinyl cyanoethyl ether) prepared inExample 1 was dissolved in 36.1 parts of an aqueous 60% solution ofsodium thiocyanate. To this solution were then added 49 parts of acopolymer containing 45% water and based on a monomer composition of:

Percent Acrylonitrile 91 Methyl acrylate 8.73 Sodium methallylsulfonate0.27

34.4 parts of water were also added and the mixture stirred to form auniform slurry. There were then added 120.5 parts of an aqueous 60%sodium thiocyanate solution and stirring was effected for minutes whilemaintaining the composition at 60 C. so as to produce a homogeneoussolution. The solution contained the acrylonitrile polymer andpoly(vinyl cyanoethyl ether) at a ratio of 98:2, respectively.

The solution was then spun into fibers following the procedure ofExample 2. The fibers obtained exhibited a K/S value of 0.759.

We claim:

1. An acrylic fiber comprising an acrylonitrile polymer of at least 70%acrylonitrile and a poly(vinyl cyanoethyl ether), said ether beingpresent in an amount ranging from about 2% to about 25%, by weight,based on the total weight of the fiber, and being distributed as aseparate phase within said fiber, said ether phase extendingcontinuously throughout the fiber length and being detached from saidacrylonitrile polymer and separated therefrom by void space, thepoly(vinyl cyanoethyl ether) being etherified with cyanoethyl groups toan extent which is between about 55% and 75% of full theoreticaletherification with acrylonitrile.

2. The fiber of claim 1 wherein the amount of poly- (vinyl cyanoethylether) in said fiber is about 10% to 15%, by weight, based on the totalweight of said fiber.

3. The fiber of claim 1 wherein the extent of etherification of saidpoly(vinyl cyanoethyl ether) is about 60% of the full theoreticaletherification with acrylonitrile.

4. A process for preparing on acrylic fiber comprising preparing ahomogeneous spinning solution in a suitable polymer solvent of anacrylonitrile polymer of at least 70% acrylonitrile and from about 2% toabout 25%, by weight, based on the total weight of polymer, of a poly(vinyl cyanoethyl ether) which is etherified to an extent which is fromabout 55% to about 75 of full theoretical etherification withacrylonitrile, wet-spinning said polymer solution into a coagulant forsaid polymers, washing the coagulated wet-gel filaments, stretching thewashed filaments and drying the stretched filaments.

5. The process of claim 4 wherein an aqueous inorganic salt solution isemployed as the polymer solvent.

6. The process of claim 4 wherein an organic solvent is employed as thepolymer solvent.

7. The process of claim 4 wherein drying of the stretched fibers is at atemperature of up to 115 C.

8. The process of claim 4 wherein partial stretching is accomplished inthe washing step.

9. The process of claim 5 wherein said aqueous inorganic salt is athiocyanate salt.

10. The process of claim 6 wherein said organic solvent is dimethylformamide.

References Cited UNITED STATES PATENTS 5/1960 Hare 260-326 2/1944 Houtz260- SAMUEL H. BLECH, Primary Examiner C. J. SECCURO, Assistant ExaminerUS. Cl. X.R.

260-2.5 ER, 898, DIG. 32; 264-182, 210 F

